Generally, the ECU for controlling the driving of various devices such as an electric motor is mounted not only in the interior, but also in the exterior of a car. This ECU is constructed by a case (hereinafter referred to as the “ECU-case”) for housing an electronic circuit (hereinafter referred to as the “ECU-circuit”) constituted by electronic parts such as CPU. The ECU-case consists of an ECU-case body, ECU-case lid covering over the ECU-case body. Harnesses for transmitting various input or output signals, cables leading to power source, and grounded wires are connected to the ECU-circuit.
The ECU has a ventilation hole (a vent) in the ECU-case to regulate the pressure within the ECU-case so as to avoid an adverse effect by thermal expansion or contraction of the air within the ECU-case. For example, an opening for penetrating harness leading to the ECU-circuit is provided in the ECU-case. A waterproof grommet is mounted in the opening of the ECU-case to enhance the sealability of the ECU-case.
The ECU is provided not only inside the cabin of a car, but also outside the cabin thereof, for example, in various places such as engine room, trunk room, and the like. In case that the ECU is provided, for example, in an engine room, enter of water, dust, and the like into the ECU case may cause of a short circuit of the ECU-circuit. Thus, the ECU-case is subjected to be sealed by filling of the sealing materials such as adhesives in the mated surfaces between the ECU-case body and the ECU-case lid.
However, the filling of sealing materials and waterproof grommet is very difficult for the perfect sealing of the ECU-case because of the following reasons.
Where self-heating of various electronical parts occur within the ECU-case or temperature of the air within an engine room fluctuate (that is, air temperature increase or decrease), the change in temperature of the air within the ECU-case or the difference in pressure of the air within the ECU-case occur in the air between the interior and the exterior of the ECU-case.
Because of the difference in pressure of the air between the interior and exterior of the ECU-case, the contaminants such as water, dust, et al would be often sucked into the ECU-case through the clearance between the waterproof grommet and the harness or through the clearance between the coating of harness and the wire. The difference in pressure of the air between the interior and the exterior of the ECU-case causes the incompleteness of the sealing materials for filling up the clearance such as the mated surface between the ECU-case body and the ECU-case lid.
Therefore, various improvements for preventing contaminants such as water, dust, and the like from entering into the ECU-case would be done and disclosed in the conventional patent literatures.
As shown in FIG. 1, Japanese Patent Laid-Open Publication No. 23636/1998 discloses an ECU constructed by double-hull structure, which the ECU-case body 101 is divided into an inner case 102 and an outer case 103 surrounding the inner case 102. The ECU-case lid 104 is mounted on the ECU-case body 101. The clearance of the mated surfaces between the ECU-case body 101 and the ECU-case lid 104 is sealed by packing and the like. The ECU-circuit is housed in the inner case 102 to be connected by a harness 105. The harness 105 connects the ECU-circuit provided in the inner case 102 through waterproof grommets 106 to the outside device. The waterproof grommets 106 are mounted in the inner case 102 and the outer case 103.
Thus, the waterproof grommet 106 is able to prevent contaminants such as water, dust, and the like from entering into the ECU-circuit in the inner case 102 because the contaminants pass through the waterproof grommet 106 to enter into the ECU-circuit within the ECU-case 102 twice.
However, Japanese Patent Laid-Open Publication No. 23636/1998 has a drawback on the ground that the ECU becomes large in size, difficult in assemblage, and costs too much in manufacturing, because of the double-hull structure of the ECU comprising the inner case 102 and the outer case 103.
As shown in FIG. 2, Japanese Patent Laid-Open Publication No. 289171/1999 discloses an ECU-case 111 manufactured by the plastics-injection mold and an earth (ground) bus-bar 112 embedded into the ECU-case 111 at the time of being injection-molded. The earth (ground) bus-bar 112 is constructed to form a pair of conductive contacts 112a, 112b for projecting inwards or outwards from the ECU-case 111, respectively. As a path between the conductive contacts 112a, 112b is formed to be electrically conductive in the earth (ground) bus-bar 112, the both conductive contacts 112a, 112b are in an electrical conduction each other. Therefore, as the earth (ground) bus-bar 112 is integrally embedded into the ECU-case 111, the clearance for harness connecting between the interior and the exterior of the ECU-case 111 does not exist and the sealing of the clearance therebetween is not required.
An ECU-circuit housed in the ECU-case 111 is connected through a grounded wire to an inner portion of the earth (ground) bus-bar 112a projecting inside the ECU-case 111, and an outer portion of the earth (ground) bus-bar 112b projecting outside the ECU-case 111 is connected through a grounded wire to an external earth (ground). Thus, a path between the ECU-circuit and the external earth (ground) has a good electrical conduction through the earth (ground) bus-bar 112. Therefore, to apply the earth (ground) bus-bar's method instead of the other harness-connection method, waterproof grommets are not required so as to prevent contaminants such as water, dust, and the like from entering into the ECU-case 111.
However, a plurality of conductive contacts, which are mutually insulated, like an earth (ground) bus-bar are required to apply this method to every harness. Thus, it has a drawback on the ground that the ECU-case becomes large. It has also a drawback on the ground that there is few freedom as for the layout of the ECU-circuit and the installation of the harness, as a position for mounting the conductive contacts projecting inside or ouside the ECU-case must be restricted by a extremely severe requirement. Further, it has a drawback on the ground that the difference in pressure between the interior and the exterior of the ECU-case causes to be the entry of water through the clearance between harness' coating and wire, and to be the breaks of sealing for the clearance of the ECU-case.
As shown in FIG. 3, Japanese Patent Laid-Open Publication No. 134939/2002 discloses the ECU-case 120 in which the clearance between an ECU-case body 121 and an ECU-case cover 122 is constructed to be sealed by filling of adhesives 123. The ECU-case 120 has a cylindrical boss 124 to form a ventilation hole 125 therein. A filter unit is mounted on top of the cylindrical boss 124 to cover the ventilation hole 125.
This filter unit is constructed by a rubber-made inner pipe 126, a fiber-made filter film 127, and a plastic barrier cap 128. The cylindrical boss 124 and the inner pipe 126 are lapped one over the other and a path 129 is formed between the inner pipe 126 and the barrier cap 128. Numeral 130 shows a connector.
In the above ECU-case 120, ventilation air can mutually communicate through a passage for communicating the interior and the exterior of the ECU-case 120, which leads from the ventilation hole 125 through fiber-made filter film 127 to the path 129. Thus, even if the changes in temperature occur in the air within the ECU-case 120, the contaminants such as water, dust, and the like would not be sucked into the ECU-case 120, as there is no differenece in pressure between the interior and the exterior of the ECU-case 120. That is, the filter unit can prevent the contaminants from entering into the ECU-case 120.
However, the filter unit is complicated in structure and the device is large in size, thus the ECU case 120 has a drawback for higher manufacturing costs.
Japanese Patent Laid-Open Publication No. 353675/2002 discloses the same ventilation system as the ECU disclosed in Japanese Patent Laid-Open Publication No. 134939/2002, but they are different from the position for mounting the ECU.
The filter unit in the Japanese Patent Laid-Open Publication No. 353675/2002 is mounted in the vicinity of electronic parts formed of exothermic element such as power transistor. Thus, it has a specific effect that the difference in temperature and pressure of the air between the interior and the exterior of the ECU-case would make it smaller, and the contaminants such as water, dust, and the like are effectively prevented from entering into the ECU-case.
However, the filter unit is complicated in structure and costs too much in manufacturing as well as Japanese Patent Laid-Open Publication No. 134939/2002. Therefore, although the ECU discloses the protective art against the invasion of contaminants such as water, dust, and the like therein, the ECU has some drawbacks.